The objective of an advanced restraint system is to provide an optimal protection system for an occupant involved in a vehicle impact. Until now, the systems involved in the task of restraining an occupant have all worked independently without any feedback between systems. A popular design uses a seat belt system that is designed to do the majority of the work of restraining an occupant. An air bag is deployed based on a vehicle crash pulse generated during a crash, which is sensed by a crash sensor. Deployment occurs at 30 ms prior to the point at which a properly seated, properly positioned occupant is expected to have moved five inches (or 500 mm). The air bag provides a restraining force that supplements the seat belt restraint.
The ideal system would have the seat belt start restraining the occupant until a certain load limit is reached. At that point, the air bag would have been deployed by the crash sensor and be ready to provide a supplemental restraining force.
To accomplish this system objective, occupant sensors have been proposed that provide feedback to a control system independently of the crash sensor and prevent or augment deployment of the air bag restraint if the occupant is out of position. However, this does not incorporate the crash sensor into a control loop, but rather the control algorithms still fire the air bag based upon the vehicle-specific 5-30 rule for time to fire (TTF), as explained above, is the crash sensor and occupant sensor work independently.
The crash sensor accelerometer does not always provide an accurate estimate of the occupant's "free body motion". Also, it is well known that crash algorithms use various integral methods to estimate occupant movement, but these estimates do not incorporate real time feedback of occupant position.
It is desirable to provide a system which more accurately determines the "free body motion" of the vehicle occupant so that the optimal firing time of the air bag can be more accurately determined.